> You create a Docker build recipe by picking a "base" GNU/Linux distribution
  > (some variant of GNU/Linux that has an absolute minimum of included programs),
  > a recipe to install build tools, and then a recipes to build the target
  > program. There are many ways to optimize this so that the result is as small
  > as possible, but that's the basics in a nutshell.

I missed the start of this thread, but I just wanted to mention that Emacs cannot build inside a docker container at the moment because of the personality syscall.

See https://debbugs.gnu.org/cgi/bugreport.cgi?bug=23529

The result of the "portable dumper" thread is likely to yield a solution to this problem (wether we end up using a portable dumper or not).

Philippe